Contralesional Trunk Rotation Dissociates Real vs. Pseudo-Visual Field Defects due to Visual Neglect in Stroke Patients

Abstract

In stroke patients, the clinical presentation of visual field defects (VFDs) is frequently accompanied by visual neglect, i.e., the inability to attend and respond to the contralesional space. However, the diagnostic discrimination between the lack of reactions to contralesional stimuli due to VFDs or visual neglect is challenging during clinical examination. This discrimination is particularly relevant, since both clinical pictures are associated with different therapeutic approaches and outcomes. The aim of this study was to systematically investigate the effectiveness of trunk rotation toward the contralesional side-a manipulation dissociating the coordinate system of the trunk from that of the head and eyes-in disentangling real VFDs from "pseudo-VFDs" that occur due to visual neglect. Twenty patients with a left-sided VFD after a right-hemispheric stroke (10 additionally showing visual neglect in neuropsychological testing, VFD + neglect; 10 without neglect, VFD) were tested with Goldmann perimetry in both standard and trunk rotation conditions. In the standard condition, both VFD and VFD + neglect patients showed a conspicuous narrowing of the left visual field. However, trunk rotation triggered strikingly different patterns of change in the two groups: it elicited a significant increase in visual field extension in the VFD + neglect group, but left visual field extension virtually unchanged in the VFD group. Our results highlight contralesional trunk rotation as a simple, viable manipulation to effectively and rapidly disentangle real VFDs from "pseudo-VFDs" (i.e., due to visual neglect) during clinical examination.

Keywords: Goldmann perimetry; stroke; visual attention; visual field defect; visual neglect.

Figure 1

Lesion overlap maps in the two groups of patients. Lesion overlap maps in the group of patients with visual field defects (VFDs) and additional neglect, as assessed by neuropsychological testing (VFD + neglect; upper row) and in the group with VFDs but no neglect (VFD; lower row). The color-coded legend at the top right of the figure depicts the number of patients in each group with damage to a specific brain region. The overlap maps are plotted onto axial slices of the ch2 template of the Montreal Neurological Institute (MNI) brain. The axial slices are oriented according to the neurological convention and are depicted in ascending steps of 10 mm. The z-position of each axial slice in the MNI Talairach stereotaxic space is indicated by the numbers at the bottom of the figure and also depicted by the blue lines on the sagittal slice on the right hand of the figure.

Figure 2

Numeric representation of the mean left visual field extension. Mean left visual field extension (calculated as the mean degrees of eccentricity within radial sectors of 15° each, defined as the space between two radial meridians; the values corresponding to the two radial sectors adjacent to the vertical meridian were excluded from analysis due to their adjacency to the midline and the right visual field; see the Section “Materials and Methods” for a detailed description), as obtained by means of conventional perimetry (dotted bars) and by means of perimetry during contralesional trunk rotation (striped bars), in the group of patients with visual field defects (VFDs) and additional neglect, as assessed by neuropsychological testing (VFD + neglect; left hand side), and in the group with VFDs but no neglect (VFD; right hand side). Please note that, after trunk rotation (eliminating the neglect component), the visual field extension in the VFD + neglect group (which was initially much smaller, i.e., 22°), became similar to the one of the VFD group (i.e., 47° and 42° respectively). The gray, dashed horizontal line represents the normal mean value of the isopter as measured in healthy individuals (75°) according to Niederhauser and Mojon (37). Error bars depict the SEM. Asterisks denote significant post hoc tests (**p < 0.001).

Figure 3

Graphic representation of the mean left visual field extension. Mean left visual field extension as obtained by means of conventional perimetry (left column) and by means of perimetry during contralesional trunk rotation (right column), in the group of patients with visual field defects (VFDs) and additional neglect, as assessed by neuropsychological testing (VFD + neglect; top row), and in the group with VFDs but no neglect (VFD; bottom row). The gray-colored surfaces represent the portions of the left visual field in which the patients gave no answer (i.e., they did not acknowledge the presence of a visual stimulus). The black, ovaloid lines represent the normal mean isopter as measured in healthy individuals, according to Niederhauser and Mojon (37).

Figure 4

Individual left visual fields in visual field defect (VFD) + neglect patients. Individual left visual fields of the 10 patients with left VFDs and additional left neglect, as assessed by neuropsychological testing (VFD + neglect; numbered I–X), measured by means of conventional perimetry (left columns) and perimetry during contralesional trunk rotation (right columns). The gray-colored surfaces represent the portions of the left visual field in which the patients gave no answer (i.e., they did not acknowledge the presence of a visual stimulus). The black, ovaloid lines represent the normal mean isopter as measured in healthy individuals, according to Niederhauser and Mojon (37). Note that perimetry during the trunk rotation condition triggered a conspicuous increase of the visual field extension in all patients.